By 2047, the only walker still in GDI service is the Mk. III Juggernaut mobile artillery system – a direct descendant of the Mk. I Juggernaut in TW2. The Mk III is based on a Mk. II Titan chassis with a new turret and crew pod, upgraded cannons, and a next generation fire control system. Because these vehicles are intended for indirect fire support and are not expected to be on the front lines, the advantages conferred by all-terrain navigation were deemed worthy of the risks.
Also check out the GDI Mammoth tank:
And GDI Firehawk:
TODO: Will add some more info later